1. Field of the Invention
This invention relates to an in-line system for sampling and adding alloying materials to a molten metal stream. The invention further relates to a method for alloying and analyzing a continuous metal stream at precise time intervals. With the present invention, castings may be changed from one alloy composition to another "on the fly", or with no substantial interruption of the basic casting process.
When continuously casting most molten metal alloys, production inefficiencies result from the need to periodically determine whether a molten composition falls within a preferred target range. Ideally, compositions should be monitored on a substantially continuous basis to assure greater uniformity in cast product. Efficiencies are further reduced when any variation from the targeted composition range occurs. Until such variations are detected and corrected, they will produce substantial quantities of undesirable metal alloy or scrap. The present invention increases casting efficiencies while also reducing the amount of scrap generated by continuous metal casting operations.
2. Technology Review
Various methods are known for analyzing or sampling cast alloys while still molten. In its simplest form, molten metal sampling may consist of removing a sufficient portion of the melt and sending it out for spectral analysis. Distant laboratory analyses produce unacceptable lags in casting time, however. Direct spectral analysis of molten metals, on the other hand, creates problems from the need to locate sensitive spectrometry equipment in immediate proximity to the casting furnaces.
An exemplary system for sampling molten metals, such as aluminum alloys, is shown in related application Ser. No. 06/826,988, the disclosure of which, including its discussion of the relevant art, is fully incorporated by reference herein. In the integrated system of this related application, a preferred method for analyzing molten metal samples is disclosed which comprises: (a) removing sample metal as a solid from a source of molten metal by immersing serrations of a rotating disc into the melt; (b) transporting the sample metal from the rotating disc to a dissolution zone; (c) dissolving the sample metal in a solvent to form dissolved sample in the dissolution zone; (d) passing the dissolved sample from the dissolution zone to an emission spectrometer; (e) vaporizing the dissolved sample in the spectrometer; (f) producing an emission spectra for the vaporized sample; and (g) comparing the emission spectra of the vaporized sample to that of a known alloy thereby determining the composition of said vaporized sample.
There is also known means by which to add alloying elements, materials or other components to a molten metal media. Eckert et al U.S. Pat. Nos. 4,688,771 and 4,689,199, for example, show a system and process for alloying certain materials to molten metal at a commercially significant rate. A preferred alloying process from the latter patent comprises: providing a body of molten metal media having an exterior and an interior surface; converting the alloying material into a superheated spray by establishing an electrical arc discharge between the interior surface of the molten media and the alloying material, said discharge being maintained with a current that exceeds the globular/spray transition current density of the alloying material; and directing the spray of superheated alloying material onto the interior media surface so as to enable dissolution and dispersion of the material into the media, the interior surface of said media being maintained a predetermined depth below the exterior surface which is sufficient for enhancing dissolution and dispersion. The disclosures of both U.S. patents, including their respective discussions of the relevant art, are also fully incorporated by reference herein.
In U.S. Pat. No. 4,765,391, there is shown an arrangement for effecting thermal analysis and molten metal modification by recording solidification data and controlling a subsequent structure-modifying process on the basis of the data obtained. The claimed arrangement consists of: a sampling container constructed such that molten metal fills the container upon immersion into the melt; means for effectively measuring and recording solidification data from one or more locations of the sample obtained with said container; means for evaluating this solidification data relative to data from a melt having a known metallurgical structure; means for controlling the supply of molten metal additions, or for subjecting the molten metal to structure-modifying measures in a controlled manner; and control means for continuously monitoring structure-modifying measures by sampling the molten metal intermittently at suitable time intervals.